NMFS Biological Opinion on U.S. Navy training ... - Govsupport.us

FINAL PROGRAMMATIC BIOLOGICAL OPINION ON U.S. NAVY ACTIVITIES IN THE HAWAII RANGE COMPLEX 2008-2013
Anti-Submarine Warfare Training Operations During RIMPAC Exercises
RIMPAC exercises have typically taken place from late June through late July. Anti-submarine exercises have
typically occurred on 21 days during this period. Multinational submarines, surface ships and aircraft typically
conduct anti-submarine warfare training against opposition submarine targets. Submarine targets typically include
real submarines, target drones that simulate the operations of an actual submarine, and opposing surface action group
— consisting of between one and five surface ships equipped with sonar — with one or more helicopters, and
maritime patrol aircraft (P-3s and P-8s) searching for submarines. RIMPAC exercises typically involve surface action
groups with each surface action group event treated as an anti-submarine warfare training event.
During a RIMPAC exercise, one or more anti-submarine warfare events may occur simultaneously within the
Hawai’ian Islands Operating Area.
Active Acoustic Devices
Tactical military sonars are designed to search for, detect, localize, classify, and track submarines. The Navy
typically employs two types of sonars during RIMPAC exercises: passive and active:
1. Passive sonars only listen to incoming sounds and, since they do not emit sound energy in the water, lack the
potential to acoustically affect the environment.
2. Active sonars generate and emit acoustic energy specifically for the purpose of obtaining information
concerning a distant object from the received and processed reflected sound energy.
The simplest active sonars emit omnidirectional pulses or “pings” and calculate the length of time the reflected
echoes return from the target object to determine the distance between the sonar source and a target. More
sophisticated active sonar emits an omnidirectional ping and then scans a steered receiving beam to calculate the
direction and distance of a target. More advanced sonars transmit multiple preformed beams, listening to echoes
from several directions simultaneously and providing efficient detection of both direction and range. The types of
sound sources that would be used in the RIMPAC exercise include:
Sonar Systems Associated with Surface Ships. A variety of surface ships participate in RIMPAC exercises, including
guided missile cruisers, destroyers, guided missile destroyers, and frigates. Some ships (e.g., aircraft carriers) do not
have any onboard active sonar systems, other than fathometers. Others, like guided missile cruisers, are equipped
with active as well as passive sonars for submarine detection and tracking. For purposes of the Navy’s analyses, 66
percent of surface ship sonars were modeled as equivalent to AN/SQS-53 and its variants having a nominal source
level of 235 decibels (dB rms ) re 1 μPa-s at 1 m 1 . The remaining 33 percent of surface ship sonars was modeled to be
AN/SQS-56 having a nominal source level of 223 dB.
1
All decibels cited in this document use the same reference unless noted otherwise
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